The condensation between an epoxide or an epoxide derivative and a cyclic anhydride has given rise to numerous works which have for example been summarized by LUSTON and VASS (Advances in Polymer Sciences 1984, Vol. 56, p. 91 and following pages) or by ISHII and SAKAI (Ring opening polymerisation, p. 13 and following pages, published by K. C. FRISCH and S. REEGEN, MARCEL DEKKER 1969).
An examination of the cited works shows that the main problem posed by this type of condensation is the homopolymerisation of the epoxide which causes the obtaining of a sequent polyether-polyester or of polymer mixtures, particularly when Lewis acids (TiCl.sub.4, BF.sub.3, etc) are used as condensation catalysts. In order to overcome this drawback, it has been suggested in prior art to utilize anionic or coordination catalysts.
FISHER (Journal of Polymer Science 1960, Vol. 44, p. 155 and following pages) has shown that the use of a tertiary amine as a condensation catalyst of an anhydride on an epoxide allows to obtain an alternate condensation.
However, this type of catalyst is ineffective as far as maleic anhydride is concerned, probably because of the complex side reactions with the amines at the level of the double maleic bond. Other types of anionic catalysts such as alkali metal salts or tetra-alkylammonium salts have also been utilized. For example WADILL, MILLIGAN and PEPPEL (Industrial and Engineering Chemistry, Product Research and Development 1964, Vol. 3, Part 1, p. 53 and following pages) describe the use of lithium chloride in the presence of protonic materials at 150.degree. C. These authors suggest that the homopolymerisation of epoxide is part of their process. As an example of a coordination catalyst, the dialkylzinc mentioned by INOUE et al. (Makromolekulare Chemie 1969, Vol. 126, p. 250 and following pages) can be cited; this type of catalyst can actually only be applied, according to INOUE et al., to phthalic anhydride. U.S. Pat. No. 4,565,845 describes the use of a catalytic system comprising an aluminium porphyrin which allows to obtain a polyester with a rather good alternation between the unit from the anhydride and that from the epoxide.
Transition metal-based catalysts have also been previously described. Thus, FISCHER (cited above) observes a partial homopolymerisation of the glycidic epoxide during its polycondensation with the phthalic anhydride in the presence of tetrabutyl titanate.
U.S. Pat. No. 3,546,176 claims the use of tetrabutyl titanate for producing unsaturated polyesters from anhydrides of unsaturated acids and from epoxides. However, as confirmed by a test carried out by the applicant and described hereafter, this catalyst does not allow to obtain a good alternation of the units from the anhydride and from the epoxide.